Act leader Rodney Hide has told Prime Minister John Key he will resign as Local Government Minister if National agrees to Maori representation on the Auckland Super City council.

Government stability would not be threatened, however, because Act's five votes would still support National on confidence and money supply votes, Mr Hide said.

The issue has been reignited after it was revealed that National MP Tau Henare sent his colleagues an email on Tuesday trying to convince them to support Maori seats in the Super City bill that will be returned to Parliament soon.

But Act's refusal to budge means that a compromise on the Maori seats that Mr Key had previously hinted at looks impossible.

Mr Hide is responsible for steering the Super City restructuring bill through Parliament. He told the Herald last night that he had made it clear to Mr Key that he could not remain as minister if the legislation included Maori seats on the council.

"But it wasn't by way of a threat," he said.

Mr Hide said he told Mr Key: "Just to be absolutely clear, you have got our support for supply and confidence but as a minister, as the Act leader, I couldn't be responsible for introducing to the House a bill that would have reserve seats in it."

Auckland-based Mr Henare is on the committee considering the bill.

His email, obtained by TV3, asks National MPs to consider a free vote on the issue of the Maori seats.

"I believe the issue is too far-reaching and too important for a party presently sitting on 1 per cent in the polls to decide alone."

The email said Mr Hide had threatened to end Act's relationship with National if Maori seats were allowed.

Maori Party co-leader Tariana Turia said last night that she was disappointed at Mr Hide's position but her party's support for the Government would not change. "We always knew when we went into this arrangement with National that there would be issues that would take us right to the wire and this is one of them.

"But we have no intentions of withdrawing support for the Government and we have no intention of withdrawing our ministerial roles. That's not what we went into the relationship for."

Meanwhile, a private member's bill promoted by Auckland-based Labour list MP Phil Twyford that would have required a referendum before any Super City assets were sold or privatised was defeated in Parliament last night at its first hurdle.